Protein misfolding and aggregation are pathological aspects of numerous neurodegenerative diseases. Aggregates of α-synuclein are major components of the Lewy bodies and Lewy neurites associated with Parkinson's disease (PD). A natively unfolded protein, α-synuclein can adopt different aggregated morphologies, including oligomers, protofibrils and fibrils. The small oligomeric aggregates have been shown to be particularly toxic.
Naturally occurring autoantibodies against α-synuclein have been detected in healthy persons and altered levels in patients were associated with particular neurodegenerative disorders; see for review Neff et al., Autoimmun. Rev. 7 (2008), 501-507. Thus, naturally occurring antibodies in patients suffering from Parkinson's disease, either spontaneously or upon vaccination, in particular in healthy patients may serve a protective role with respect to α-synuclein aggregation; see, e.g., Woulfe et al., Neurology 58 (2002), 1435-1436 and Papachroni et al., J. Neurochem. 101 (2007), 749-756. Hitherto, the therapeutic significance of autoantibodies had been difficult to assess. This is mostly due to the lack of straightforward experimental approaches for their isolation and subsequent characterization in vitro.
Recently, oligomeric species of α-synuclein have been reported extracellularly in plasma and CSF (El-Agnaf et al., FASEB J. 20 (2006), 419-425) and immunization studies in mouse models of PD show that extracellular mouse monoclonal antibodies against α-synuclein can reduce accumulation of intracellular α-synuclein aggregates (Masliah et al., Neuron, 46 (2005), 857-868) supporting the idea that antibodies that neutralize the neurotoxic aggregates without interfering with beneficial functions of monomeric α-synuclein may be useful therapeutics. However, the therapeutic utility of murine based antibodies in human is hampered by the human anti-mouse antibody (HAMA) response in view of their non-human origin.
Emadi et al. in J. Mol. Biol. 368 (2007), 1132-1144, describe the isolation of single chain antibody fragments (scFvs) from a phage displayed antibody library based on human sequences against α-synuclein, which bind only to an oligomeric form of α-synuclein and inhibit both aggregation and toxicity of α-synuclein in vitro. However, although the generation of scFvs from phage display is rather simple, this technique has severe drawbacks since the antibodies so produced bear the risk of undesired crossreactivity against self-antigens and lack the characteristics of evolutionary optimized natural human antibodies produced by the human immune system. Furthermore, such antibodies may not be specific enough because of cross-reactivity with other proteins and/or with the target protein in context with normal physiological environment and function. In case of Parkinson's disease, for example, antibodies that also cross-react with physiological derivatives of α-synuclein bear the potential to cause side effects related to the normal functions of the physiologic target structures. In this respect, an undesired autoimmune disease would downrightly be induced—a hardly calculable risk also in the conceptual design of active immunization experiments employing protein structures that, in variant form, also occur physiologically.
More recently, Seitz et al. (81. Kongress der Deutschen Gesellschaft für Neurologie mit Fortbildungsakademie Hamburg 10.-13.09.2008), reported on the isolation of anti-α-synuclein polyclonal autoantibody from different immunoglobulin solutions and samples of single blood donors through affinity chromatography. However, besides the fact that this approach provides mere limited amounts of the desired antibody, polyclonal antibodies are of only limited use for therapeutic application, for example because of their heterogeneity and the risk of being contaminated with other α-synuclein associated molecules which have undesired side effects. Likewise, the diagnostic value of polyclonal antibodies is reduced since the variability of the composition of the antibodies will influence the overall specificity and reactivity. This is all the more true for antibodies against proteins subject of aggregation and deposition due to misfolding.
Thus, there is a need to overcome the above-described limitations and to provide a therapeutic and diagnostic human antibody against α-synuclein.